HYDROGENATION OF THIN Y-BA-CU-O FILMS - ELECTRICAL-TRANSPORT AND STRUCTURE PROPERTIES OF YBA2CU3O7 AND YBA2CU4O8

c-axis-oriented YBa2Cu3O7 (1:2:3) and YBa2Cu4O8 (1:2:4) thin films were charged with hydrogen at 463 K and a H-2 pressure of 100 mbar. The hydrogen concentrations and depth profiles were measured with the N-15 nuclear reaction method. In contrast to earlier studies on bulk samples where a constant T(c, onset) is reported, we find in our 1:2:3 films that the superconducting transition temperature decreases continuously with increasing hydrogen concentration and that the transitions remain relatively sharp, e.g., T(c, onset) 38 K and DELTAT(c) = 6.2 K for [H]/cell congruent-to 0.6. The electrical resistivity and Hall-effect measurements in the normal state indicate that the main effect of hydrogen doping is a reduction of the charge carrier concentration, whereas the carrier mobility is not changed significantly. At an average hydrogen concentration of [H]/cell congruent-to 2 in both systems, a new hydride phase is observed, which for 1:2:3 is characterized by a c-axis expansion of 16% and for 1:2:4 by a c-axis expansion of 1.5%.